This invention relates to the field of optics and, more particularly, to an optical relay for sampling or concentrating incident light without substantial loss of illumination.
In various optical systems it is desirable to sample a continuous image so that its elemental constituents can be put into discrete form for subsequent processing. A number of image detection and processing equipments would benefit from an efficiently sampled image. For example, there is an increasing availability of a type of solid state image detectors wherein only a portion of each elemental area of detector array is "active," and light incident on inactive portions is effectively wasted. In other applications it is useful to have a number of images share a single image plane, such as a photosensitive surface. For example, "image multiplexing" may involve storing multiple images on a single frame of photographic film, e.g., for color multiplexing on black and white film. Also, optical data processing or analysis may involve the incidence of multiple images on a camera tube.
In any system for image sampling or multiplexing it is desirable to optimize parameters such as resolution and efficiency of light collection, but it is often found that severe tradeoffs exist which compromise the quality of one or more important performance factors. As a simplified illustration, one way to sample an image is by placing a pinhole array over the image so that the light passing through each pinhole is a measure of the image density at the pinhole. In this type of system, the efficiency of light collection is quite poor because most of the light will be blocked by the opaque portion of the pinhole array. One technique for increasing the efficiency of such a system is to increase the size of the pinholes. However, this adversely affects system resolution by introducing uncertainty as to the location of the sampled image values. Both efficiency and resolution of sampled values are substantially improved by interposing a small lens at the position of each enlarged pinhole, thereby effectively converting the array into a "fly's eye" lens array. in such case, each individual lens element or "lenslet" collects light over its entire area and focuses it to a point in the detector plane. One problem with "fly's eye" arrays, however, is that it is difficult to produce lens arrays having elements small enough to sample at the increments required for optical images. Also, as the lenses are made smaller and smaller the requirements for spacing of the optical elements (such as the spacing between lens array and detector) become exceedingly small and impractical.
It is an object of the present invention to provide solution to the prior art problems as set forth.